On Tuesday, news site The Register published a story containing explosive "above top secret" information about Britain's surveillance programs, including details of a "clandestine British base tapping undersea cables in the Middle East." Reporter Duncan Campbell, who wrote the story, said it was based on documents "leaked by fugitive NSA sysadmin Edward Snowden" that other news outlets had declined to publish. 

However, it's not necessarily clear how Campbell got his hands on Snowden's document stash. 

Glenn Greenwald, who published the first stories based on Snowden's documents in The Guardian, told Business Insider on Tuesday that Snowden has "no source relationship" with Campbell.

"Snowden has no source relationship with Duncan (who is a great journalist), and never provided documents to him directly or indirectly, as Snowden has made clear," Greenwald said in an email. "I can engage in informed speculation about how Duncan got this document — it's certainly a document that several people in the Guardian UK possessed — but how he got it is something only he can answer."

For his part, Campbell is not interested in discussing how he got the documents used for his story.

"Journalists in the UK — just as in the US — do not reveal their sources, or respond to questions as to confidential sources. We protect them. That is our obligation and our duty," Campbell wrote in an email to Business Insider.

This isn't the first story Campbell has published allegedly based on Snowden documents. Last August, Campbell wrote a piece for The Independent about the secret British surveillance base. In that article, Campbell suggested The Guardian "agreed to the Government’s request not to publish any material contained in the Snowden documents that could damage national security," including the existence of the surveillance base.

Greenwald responded with a column that included a statement from Snowden saying he had not worked with Campbell and speculating the documents were actually by the British government as part of an attempt to make the case his leaks were "harmful."

In addition to Snowden's theory that Campbell may have obtained documents from a government source, it also seems possible he was leaked information by a Guardian staffer with access to the documents. Business Insider asked Guardian editor Alan Rusbridger about this possibility on Tuesday and received a response from a representative for the paper who said they have no idea how Campbell obtained any of Snowden's documents. 

"We don't know who Mr Campbell's source is. We have always been open and transparent about all of our reporting partners," the representative  said. 

So it seems someone out there is in possession of Snowden documents other newspapers have declined to publish and is eager to release them. In other words, the Snowden leaks have leaked.

[UPDATE 20:45 EDT] Duncan Campbell told Wired UK that he " was able to look at some of the material provided in Britain to the Guardian  by Edward Snowden last year."

Campbell, who has been reporting about Britain's signals intelligence agency (GCHQ) for more than 30 years,  would not answer a question about whether he has copies of the relevant documents.